1. Field of the Disclosure
The present disclosure relates to communication systems and, more specifically, the present disclosure relates to systems and techniques for locating the position of a wireless communication device in a Code Division Multiple Access system.
2. Description of the Related Art
Mobile communications networks are in the process of offering increasingly sophisticated capabilities for locating the position of a mobile terminal of the network. The regulatory requirements of a jurisdiction may require a network operator to report the location of a mobile terminal when the mobile terminal places a call to an emergency service, such as a 911 call in the United States. In a Code Division Multiple Access (CDMA) digital cellular network, the position location capability can be provided by Advanced Forward Link Trilateration (AFLT), a technique that computes the location of the mobile station (MS) from the mobile station's measured time of arrival of radio signals from the base stations (BS). A more advanced technique is hybrid position location, where the mobile station employs a Global Positioning System (GPS) receiver and the position is computed based on both AFLT and GPS measurements. A further application of the hybrid technique is when time obtained from a GPS-synchronous cellular network is used in obtaining the GPS measurements and computing the mobile station's position.
Currently, GPS receivers are being incorporated into mobile terminals in order to increase the accuracy of mobile terminal location determination. The GPS receivers can be autonomous and perform all GPS acquisition functions and position calculations (also know as standalone), or they can be non-autonomous (also known as wireless assisted) and rely on the cellular network for providing GPS acquisition data and possibly performing the position calculations. By receiving GPS aiding data from the network, a mobile terminal with GPS capability can obtain the time and position data from the GPS satellites in about 10 seconds or less, during a typical phone call. Many, if not most, CDMA wireless phones having GPS capability are expected to be wireless assisted GPS receivers having hybrid capability of providing both GPS and AFLT position information upon the request of a serving base station handling a call from the wireless phone. The position location session can be MS-assisted or MS-based, depending on where the position computation takes place. In the MS-assisted case, the mobile station sends back raw or pre-processed measurement data to the base station. A network entity then computes the location. In the MS-based case, the position computation is performed in the mobile station.
Message protocols and formats for CDMA position location employing AFLT, GPS and hybrid receivers, applicable to both the MS-based and MS-assisted cases, have been published in TIA/EIA standard IS-801-1 2001, Position Determination Service Standard for Dual-Mode Spread Spectrum Systems.
Another position location technique is where the measurements are made by a network entity, rather than the mobile station. An example of these network-based methods is the RTD measurement carried out by the serving base stations. Measurements made by the mobile station may be combined with network-based measurements to enhance the availability and accuracy of the computed positions.